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Ann. Geophys., 21, 2059-2072, 2003
www.ann-geophys.net/21/2059/2003/
© European Geosciences Union 2003
The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data
P. Janhunen1, A. Olsson2, and W. K. Peterson3
1Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland
2Swedish Insititute of Space Physics, Uppsala Division, Uppsala, Sweden
3LASP, University of Colorado, Boulder, Colorado, USA
Abstract. We study the occurrence
frequency of upward auroral ion beams as a function of altitude using three
years of Polar/TIMAS ion data combined with 11 years of DE-1/ EICS ion
data, in order to reach a complete altitude coverage between 5000 and 30 000
km. The most interesting result is that there is a peak in ion beam occurrence
frequency and invariant energy flux and invariant particle flux at ¢ 3 RE
radial distance. The peak exists at about the same altitude in both the evening
and midnight MLT sectors. No solar cycle effects are found. We suggest that the
peak could be due to a preferred altitude of auroral potential structures at ¢
3 RE . To substantiate the suggestion, we also present a simple Monte Carlo
simulation of ion beams. Another result is that the ion beam occurrence
frequency and invariant (mapped to ionospheric altitude) energy and particle
fluxes increase in the radial distance range 4–6 RE , suggesting that wave
heating processes may take place in this altitude range.
Key words. Magnetospheric physics (auroral
phenomena; magnetosphere-ionosphere interactions) – Space plasma physics
(charged particle motion and acceleration)
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